1. Field
The disclosure relates to the field of the manufacture of rubber items intended for example to form the reinforcing elements of a tire.
2. Description of Related Art
These reinforcing elements as a general rule are made up of lengths of reinforcing thread coated in rubber, said lengths being parallel to one another and making a given angle with the circumferential direction of the tire. Thus, in a radial tire, the carcass reinforcing threads make an angle of 90° with the circumferential direction. Likewise, the reinforcing plies that make up the crown belt are made up of reinforcing threads that make an angle comprised between 25° and 45° with the circumferential direction. Finally, the hooping plies, when these are not obtained as continuous strips wound in a number of turns, are formed of lengths of reinforcing threads wound over one or two turns and forming a zero angle with the circumferential direction.
It is fairly common practice in the tire industry for these various components themselves to be produced by cutting them from continuous plies, formed of continuous reinforcing threads coated with rubber, which are parallel to one another and make a zero angle with the longitudinal direction of the said continuous ply, also referred to as a straight thread ply.
A straight thread ply is manufactured as a general rule using a calender comprising at least two rotary calendering rolls, through the nip between which a ply of continuous reinforcing threads evenly spaced apart and interposed between two continuous sheets of rubber passes. As they pass through the nip between the calendering rolls, the sheets of rubber are pressed against one another and feed the spaces between the reinforcing threads to form a composite assembly of reinforcing threads and of rubber.
In order to ensure good distribution of material, the sheets of rubber have a width slightly greater than the width of the ply of reinforcing threads. The result of this is that lateral selvedges are formed where the sheets of rubber do not trap any thread between them. Therefore, a selvedge cutting and recycling device is provided downstream of the calendering means so that the composite ply can be cut to the precise width of the ply of reinforcing threads.
However, it is found that the pressing-together of the sheets of rubber at the selvedges is achieved imperfectly quite simply because of the lack of volume of reinforcing threads in this zone. This imperfect pressing results in poor cohesion of the sheets of rubber at the selvedges, leading to irregularities at the cutting device intended to remove the selvedges.